The present invention is directed to mechano-acoustic pianos of the type having tone-generating elements in the form of struck strings made of steel core wire stretched under tension. The strings are either plain or wrapped with one or more layers of covering wire, each layer encircling the core wire in the form of a multi-turn helix. The piano has 88 notes, a key for each note, a hammer for each note and a compass spanning at least the frequency range from the note AO=27.5 Hz to the note C8=4186 Hz.
According to references describing the history and early development of the piano and its forerunners, the earliest designers of keyboard instruments were unaware of the importance of the relationship between the striking distance (d) and the speaking length (L) for each string. The striking distance of each string is that distance from the string plate vibrational termination of the string to the point at which the hammer hits it. The speaking length of each string is its length between its vibrational terminations. This relationship can be expressed as the ratio d/L. Consequently, this relationship was ignored or disregarded in the instruments the early designers built. This fact is verified in William Braid White, Theory and Practice of Pianoforte Building (New York: Edward Lyman Bill, circa 1909), p. 34 and Rosamond E. M. Harding, The Pianoforte (New York: Da Capo Press, 1973; original publication 1933), p. 64. In due time, however, it was discovered that the value of d/L influences profoundly the performance of the instrument, and efforts were made to produce instruments in which the value of d/L was set within the range considered to produce optimum performance. According to abundant references in the literature the optimum value for d/L in pianos is universally believed to lie within the range between 1/7 and 1/9. That is, it was concluded and has been accepted for a very long time that pianos sound best when the hammers strike the strings at a point between 1/7 and 1/9 of their speaking length. (Decimally, this range is approximately 0.143-0.111.) This range is discussed in numerous publications of which the following are exemplary: W. V. McFerrin, The Piano--Its Acoustics (Boston: Turners Supply Co., 1972), p. 19; Edgar Brinsmead, The History of the Pianoforte, (Detroit: Singing Tree Press, 1969; original publication London: Ewer and Co., 1879), p. 47; Edwin M. Good, Giraffes, Black Dragons, and Other Pianos (Palo Alto: Stanford University Press, 1982), p. 9; Otto Ortman, The Physical Basis of Piano Touch and Tone (New York: Dutton and Co. 1925), p. 96. That this belief is carried out in the acatual practice of manufacturing pianos is confirmed by inspection of various instruments. In contemporary pianos built according to the prior art, the only known exception to the 1/7 to 1/9 rule occurs in the extreme treble of the instrument, where, in order to produce maximum sound output, it has been found to be necssary to reduce d/L to a value smaller than 1/9. Values as small as 1/20 (0.05 if expressed decimally) have been found to be required. But this practice also is familiar to all piano designers, and is accepted as a standard design practice.
The present invention is based upon the discovery that the tone quality of the bass portion of the scale of some pianos can be improved by increasing the value of d/L of at least some of the notes to a value greater than 1/7. The findings are that values of d/L between 1/7 and 1/5 produce the best results. It also has been determined that the optimum value of d/L depends upon the frequency of the particular note in question and also upon the design parameters of each particular string. This finding is in contrast to conventional prior art design procedure in which it is normally considered desirable to design the entire bass portion of the scale so as to have the same value of d/L for all of the bass strings. In contrast to this standard practice, it has been found that in order for each note to have the best tone quality, it is desirable to determine the optimum value of d/L for each string individually. The optimum values found for the strings of adjacent notes on the scale generally will not be very much different from each other, but will seldom be exactly the same. In addition, it has been determined that the optimum value of d/L depends on the parameters of the string such as its length, its tension, the sizes of wire used to fabricate the string, and on the resulting inherent inharmonicity of the string. In general, the optimum value of d/L for a particular note on the scale will increase as the size of the instrument decreases. That is, small pianos with their shorter strings will require larger values of d/L than larger pianos. This appears to result from the greater inharmonicity of the shorter strings. To give an idea of the amount of this difference by numerical example, it has been found in one case that a No. 1 string of speaking length 210.3 cm for a large grand piano, tuned to a freqeuncy of 27.5 Hz, required a d/L of 0.158 for optimum tone, while a No. 1 string 122.2 cm long, for an upright piano of medium size, tuned to the same frequency, required a d/L of approximately 0.172 for optimum results.
The phrase "bass portion" as used herein and in the claims refers to those notes of the scale, the strings of which terminate on the bass bridge. The number of strings which terminate on the bass bridge of a piano varies considerably depending upon the nature of the piano. Generally, the number of such strings falls within the range of from about 17 strings to about 32 strings.